More studies on the PVAl+H3PO2+H2O proton conductor gels

Solid polymer proton conductors made of poly(vinyl alcohol) (PVAl), hypopho sphorous acid (H3PO2) and water with conductivities as high as 0.1 S cm(-1) at room temperature were studied by means of differential scanning calorim etry (DSC), X-ray diffraction and thermogravimetry (TG). The DSC curves for membranes with the highest acid concentrations show on heating a very low glass transition temperature (revealing a separate acid/water phase), a col d crystallization after this glass transition, a melting of crystallizes or of the freezing water in the polymer network and a recrystallization above ambient temperatures as the membranes lose water. The X-ray spectra for th e raw samples at room temperature indicate that the amorphousness of PVAl c omplexes increases with the concentration of H3PO2; but its degree of cryst allinity increases with the annealing time of samples above room temperatur e. The TG traces confirm that membranes with the highest acid concentration s have the highest water content and that the maximum rate of water removal is at about 50 degrees C for all samples. (C) 2000 Elsevier Science Ltd. A ll rights reserved.